1. Field of the Invention
The present invention generally relates to methods and apparatuses for measuring remaining coulombs of electrical energy storage devices, and more particularly to a measuring method and a measuring apparatus for measuring remaining coulomb of a rechargeable battery charge in an electronic device.
2. Description of Related Art
Electrical energy storage devices, especially rechargeable batteries, such as nickel-hydrogen storage batteries, lithium-ion batteries, etc., are widely used as power sources for various electronic devices. After a rechargeable battery has been fully charged, a maximum coulomb is obtained. When the charged battery discharges over a time interval, the maximum coulomb decreases to a remaining coulomb. If the remaining coulomb is too small, an electronic device using the rechargeable battery as a power source may not work. Therefore, it is required to timely measure the remaining coulomb of the rechargeable battery.
Currently, two conventional methods for measuring the remaining coulomb are used, i.e., a current integrating method and a terminal voltage measuring method.
The current integrating method generally includes following steps of: storing an initial charged coulomb of a charged battery; discharging the charged battery; taking the integral of a discharging current to calculate a discharged coulomb; and identifying the remaining coulomb by subtracting the discharged coulomb from the initial charged coulomb. However, internal chemistry reactions exist in the charged battery. The internal chemistry reactions leads to self-discharges in the charged battery, the initial charged coulomb is thus inaccurate. Therefore, it is difficult to get an accurate remaining coulomb based on the inaccurate initial charged coulomb.
The voltage measuring method includes following steps: detecting relationships of various standard voltages of the rechargeable battery and corresponding standard remaining capacities, and storing the relationships in a rechargeable battery before marketing; measuring an actual voltage of a load which is connected to the rechargeable battery; and determining an actual remaining coulomb corresponding to the measured actual voltage according to the relationship of voltages and capacities. However, there are also two factors influencing a veracity of the measured voltage. One factor is that an actual measured voltage of the load is only part of an ideal measured voltage, and the other part of the ideal measured voltage is skewed by the rechargeable battery itself due to an essential resistance thereof. Therefore, according to the relationships of voltages and capacities, the remaining coulomb corresponding to the actual measured voltages is less than an ideal charge corresponding to the ideal measured voltage. The other factor is that the rechargeable battery is gradually worn out by repeating charges and discharges, so that the relationships of voltages and capacities are variational. Therefore, it is also inaccurate to use the voltage measuring method to measure the remaining coulomb.
Therefore, a measuring method and a measuring apparatus for measuring remaining coulomb are needed in the industry to address the aforementioned deficiencies and inadequacies.